Pattern design — draft allowances by material: Compared with wooden patterns, metal patterns (e.g., aluminium) generally require what magnitude of draft allowance on vertical faces for easy withdrawal from sand moulds?

Introduction / Context:
Draft is the taper provided on pattern faces parallel to the direction of withdrawal to facilitate clean release from the mould and prevent edge damage. The required draft depends on pattern material, surface finish, and moulding process. This question contrasts metal and wooden patterns.

Given Data / Assumptions:

• Smooth, rigid metal patterns (e.g., aluminium or bronze) versus wooden patterns.
• Sand moulding using typical binders and permeability.
• Goal: minimise sticking and erosion during draw.

Concept / Approach:
Metal patterns typically have superior surface finish and dimensional stability compared with wood. They are less prone to swelling, warping, or surface roughness. As a result, lower draft angles are sufficient to ensure release from the sand. Wooden patterns, being rougher and more compliant, generally require higher draft to avoid tearing the mould.

Step-by-Step Solution:
Assess surface finish and rigidity: metals have smoother, stiffer faces.Lower friction and reduced tendency to stick allow smaller draft.Therefore, relative to wood, metal patterns require less draft.Apply process-specific guidelines to choose exact degrees (often 0.5–1.0% for metal vs. higher for wood).

Verification / Alternative check:
Foundry design tables list smaller recommended draft for metal patterns, confirming the relationship.

Why Other Options Are Wrong:
“More” contradicts improved release characteristics of metal patterns.

“Same” ignores material and finish effects.

“No draft” is risky; some draft is almost always recommended.

Reverse draft would trap the pattern in the mould.

Common Pitfalls:
Neglecting mould hardness and moisture, which affect draw; forgetting that textured or knurled pattern areas may still need extra draft; overlooking core print draft requirements.

Final Answer:
less